The City of Hope presently does not have a scanning electron microscope. Our research projects have proceeded to a point where scanning electron microscopy is required. The benefit of the SEM to five research projects (4 supported by NIH and 1 supported by NSF) is described in this application. The problems of the research projects in which the SEM will be utilized are: 1. A study to make an accurate quantitative determination of the number of synapses on crustacean stretch receptor neurons; the only known material which provides favorable conditions for physiological work in vitro on inhibitory transmission at a single, isolated neuron (Ikeda). 2. Studies to look for a predicted preferential orientation of dendrites to neuropil regions that are "rich" in potential synaptic axon terminals in the developing central nervous system and to examine the developmental differences of motor neuronal dendrites in three genetically different strains of mice (Vaughn). 3. Studies of the cerebrovasculature concentrating primarily on the microvascular endothelium, but also investigating the innervation of intraparenchymal brain vessels (Roberts and Krause). 4. Studies of synaptic supramolecular structure in the mammalian central nervous system and in electroplax of Torpedo californica utilizing immunocytochemical techniques (Flanagan and Lindsey). 5. Studies of developmentally expressed cell surface markers on differentiating red blood cells and of crossreacting antigens on ontogenetically related tissues (Miller). Both the principal investigator and Dr. Junzo Desaki, a visiting scientist in the Division on Neurosciences, have considerable expertise in scanning electron microscopy and are available to guide and assist the major user group in the scanning electron microscopy necessary for the described projects. The City of Hope has committed continued support for utilization and maintenance of the scanning electron microscope laboratory and an organizational plan for administration of the laboratory has been developed.